Differential screw adjustment for magnetic core air gaps



v- 1952 R. e. scHLAwm DIFFERENTIAL SCREW ADJUSTMENT FOR MAGNETIC COREAIR GAPS Filed Sept. 8, 1949 .m ..W P h to ns we H m a Q His Attorney.

Patented Nov. 4, 1952 I2,s17'-,69'2 DIFFERENT-11in sjonnw ADJUSTMENT FORMAGNETIC eons AIR GAPS ii'e'ipn jsei iewis, rittsfieni, Mass assigner rGenerainmefi-ie Gom'pany; a eorpo'i'atio'ii of New Ybi-k' Application Seiteinber 8, 1949, Serial No. 111 431 invention relates to 'stationar'fielectrical in da mon apparatus, and more particular}? to magnetic coresof the type havihg adjustable air jgjap s. In the construction oi s'oihetithes or 'eieeti'ibal reactors, it is common tribute to bfovide themagnetic core of the reactor with an air gap, in order to obtain certaindesired i'n'aghti'c' chara'c te'ris t ics. Where the ifea'ctahe'valiieof the reactor must be held within 'a predetermined close tolerance,this value is very often obtained by adjustinent of the air gap in themagnetic core. This adjustment is norma ly ihade by the addition ofspacer file'rnbeis nntil the thickness of the air ap has been changedsi'ifiiciently to give the desired value of reactane'e. However, due tothe fact that the change in thickhess of the air gap which is involvedis geneieny 'of the magnitude Of several thou's'andths of an inch,cnidefable dihiculty is sometimes experienced in maehining spacers ofthe requisite dimensions.

It is an object or my invention to provide a device integral with thereactor strlicture' for varymg the thickness of the reactor air gapwithin very close tolerance's.

It is a further object of my invention to eliminate the hefi'S'Sit'yreiil's'in'g sp'aee'rs in order to adiust theeir gap of a magneticreactor.

In aeeem nenmem of these ob'j'ebtite's, invention brovides a createintegral with a ihanetie core which provides for adifi's'tfi'i'erit 6fthe airgap within close to'lrahc'es means of a. differential motiohbetween a threaded 'stiid attaohed to one etter the in'aiitie care, andexternally threaded screw haviiig a tabbed en'a threaded akial holewithin when the stud motes. This screw has threads of diilreiitbitchs onits external and in'tr'nal 's1'1i"fa' es Motib'n of the screw with resbect to the reactor casing on excr'n'ei thread causes an egspeeite mate's6f the threaded stiid along are drilled and thieaded 'akis of the screw.The 's'tiid and Saree have in espes 'ite directions, with the net changethe air gap being the iiiffiehee between these memetions.

The feat ires rjih s ii jeiit oi jvhieh I believeto be novel are setforth with fiart'icfilarity in the appended claims, My invention itselfhoweve r, both as to its organization and se, together with furtherobjects andadvantagesthereo f, may best be understood by reference tothe following description taken in conneqtion with the accompanyingdrawing in which Figs, 1 and; represent respectively a top plan view anda front elevation view of a magnetic core embodying the air gapadjusting means of my invention; while Fig. 3

rebresents a p rs eemve View partially cut away, of a section or themagnetic core containing the embodiment of my invention.

Referring to Figs. 1 and 2, there is sh'ow'fi therein a reaetor Ieoifip'ri'sing' a laminated meg= netic core having two approiiifnatelyrectangular core seetre'ns 2 and 3 wh'ih are held together to form aunitary 'r'nagnetic stri'i'ttu'e 153} means of bfolt s o'r rivets '4 and5. Co're sections 2 3' are each respectively formed by bending apliiralit'y of strips 0i magnetic rfiaterial or by spirally wind-- ih'ga single strip 'b'f in'agneti material about a suitable mandrel ofrectangular shape. One leg' of each of the respective co'r'e sections isslotted at a ip'rokimatelv its midpoint to provide ah air gap.

The two -r'ectanj'gular core sections 2 and '3 have their respectiveslotted legs adjacent to one another, being separated only by aninterposed brace or tie-plate member to be H reinafter aeserited. Thatis, leg sections 6a, '6?) of core section '2 are reseeetive1-51 edjeeemle'g sections Ta, 1 er eq're section 3. These adj acen't leg sections6a, 6b, 1a. Tb together constitute the center leg of the re e'eg-Adjacent iee sections ta, 1d are 'sehafated' from adjacent leg seetions6b, U) by 'air 'gap 8. A cylindrical winding!) is placed about this cener leg. Suitable supporting means 8a is provided adjacent the upper andlower surfaces er windme 9.

A meta enea's'ing an clamping means {0 is provided fh'i the magneticcore arid is comprised er an upper seamen n and a lower section '12.These two sections are relatively movable with re=- -s'petit 'to'bn'eanother, and may be clamped t0= gethe'r b'y'bolts l3 a'h'd "I 3, therebyCompressing the laminated magnetic'coie inside of the clamping andene'azsme means In. t P

In'aecorda'nce with'ni'y invention, the thickness of the air gap 8 isveriea by moving the two se'c= tions of the center leg on opposite sidesof the air gap with iestee't to one another by a device which integralwith the care and clamp "structure, 11; e here nafter described. In theconstrue tion illustrated in the drawing, the lower half of the centerleg 'Co'mfiiiSed of Sections 617, 11) below a r gap 8 is stationary'with respect to the claniping "stfutiiie in, while the upp'erha'lf 6a,1a '0 f the center or'e leg is "friov able with respect to thecla'fnbing striitii'i ID. This relative iii'o'tion between the upperseame 6d, la and the lower seamen 6b, t or the center core Ie'g'her'mits a venet an or the "air gap.

;The 16we'r half '61), 11) '6f the Center c'd'r'e 'le'g be w the air apis i'igidfi' ettaehe'a by means eff-a ie-plate or trace member [5 to aweek is which is rigidly mounted in the center of the top surface ofupper clamping member I'I. Tie-plate or brace member I is of S-shape andis positioned in the center of the center core leg between the adjacentsurfaces of core sections 2 and 3. Rivet 5, which, as has beenpreviously mentioned, holds legs 6b, 1b of core elements 2 and 3together to form the lower portion of the center leg, also passesthrough tie-plate I5 which is interposed between the adjacent surfacesof leg sections 6b, 1b. The two outer edges of tie-plate I5 arerespectively bent in oppositely-disposed right angles to its centerportion, thereby giving member I5 its 8 configuration, and alsoproviding a suitable surface through which screws I! can pass in orderto rigidly attach tie-plate I5 to block IS on the upper surface ofclamping member I I.

As can best be seen in Fig. 3, slightly more than the upper half of theinterposed surface of tieplate I5 between center leg sections 601., la,is cut away in order to permit the interposition of rectangular steelstrip I8 which is rigidly fastened at its lower end to the lower end ofleg members 60., la by means of rivet 4, which also serves to hold legmembers Ba, Ia rigidly together.

In accordance with my invention, the upper portion of steel strip I8 isfastened rigidly by some suitable method, such as welding, for example,

to the lower end of stud [9. The upper portion of stud I9 is threadedexternally and is in engagement with the internal threads of axiallydrilled and threaded screw 20. The screw 20 has a hole drilled throughits center axis, and this hole is threaded with a thread of the samepitch as that on the outer external surface of stud I9, so that stud I8and the threaded axial drilled hole of screw 20 are in threadedengagement. The outer surface of screw '20 is also threaded, but has athread of a different pitch than that of the threaded hole through itscenter axis. This external thread of a different pitch than thatof thethreadternal thread drilled hole 2I in block I6. To facilitate assemblyoperations, block I5 is split into an upper and a lower section, withthe upper section being threaded to receive screw 20. The two sectionsof block I6 are held together by screws 22.

In adjusting the air gap 8, screw 20 is turned by means of slot 23 inits upper surface. When screw 20 is turned in a clockwise direction, forexample, and assuming that all threads are righthand threads, theclockwise motion of screw 20 causes it to move downward to the extent ofone thread pitch, and if this were all that were involved, the uppersection 6a, Ia of the center core leg would move downwardly acorresponding amount since the stud I9 axially positioned in screw 2i]is connected to center leg section 6a, Ia. by means of steel strip I8.However, as has been mentioned before, threaded stud I9 is in engagementwith the axially drilled threaded hole in screw 20. Consequently, adownward motion of screw 20 will cause an upward motion of threaded studI8, to the extent of one thread pitch. However, the thread pitch of thestud I3 is a different value than that of the outer threaded surface ofscrew 20. Consequently, there will be a diiferential between these twoopposing motions, so that the net motion will be the difference betweenthe two thread pitches.

Using concrete values for illustrative purposes, assume that the outersurface of screw 20 has ten threads per inch, and that the threaded studhas eighteen threads per inch. Then, it can be seen that a clockwisemovement of screw 20 of one turn will cause it to have downward motionof one-tenth of an inch. At the same time, however, the threaded studwill move upwardly oneeighteenth of an inch. The net motion of the studI9, the steel strip I8, and the upper portion 6a, 6b of the center legof the magnetic core, will be inch- A inch=.044 l inch downward. Thereverse is true when the slotted screw is turned in the oppositedirection.

It can be seen, therefore, that my invention provides an easy andconvenient means for adjusting the air gap of a magnetic core. Itpermits adjustment within very narrow tolerances, and in very smallincrements, due to the difierential motion between the screw 20 and thestud I9, as as hereinbefore described. This permits adjustment of thereactance values within very close limits, by adjustment of the air gapusing the device which I have disclosed.

While there has been; shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications can be made therein Without departing from theinvention and, therefore, it is aimed in the appended claims to coverall such changes and modifications as fall within the true spirit andscope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a. magnetic core comprising two generally rectangular-shapedmagnetic hollow core sections formed of bent strip magnetic material,each of said sections having one leg thereof adjacent one leg of theother section to form a composite center winding leg about which anelectrical winding is placed, an encasing means surrounding saidmagnetic core, an air gap intermediate of the length of said centerwinding leg, means for adjusting the thickness of said air gapcomprising a metallic strip having one end attached to one section ofsaid center leg on one side of said air gap, said metallic strip beingpositioned intermediate the adjacent legs of said core sections, a studrigidly attached to the other end of said metallic strip, an externallythreaded screw rotatable in said casing, said screw also being'axiallydrilled and threaded, the axial threads and external threads of saidscrew being of different pitch, said stud being threaded at one end andengageable with the axial threads of said screw, rotation of said screwon its external threads to cause axial advancement of said screw in onedirection causing axial motion of said stud in an opposite direction,thereby causing a motion of said section of said center leg attached tosaid metallic strip equal to the differential motion between said screwand said stud.

2. In a laminated magnetic core comprising two magnetic core sections ofsubstantially hollow rectangular shape and formed of bent strip magneticmaterial, said core sections each having one leg adjacent one leg of theother core section to thereby form a center winding leg about which anelectrical winding may be placed, said center winding leg being providedwith an air gap intermediate of its length, means for adjusting thethickness of said air gap comprising a casing enclosing said magneticcore, an externally threaded screw threadedly movable in said casing,said screw also being drilled and threaded axially, the external andinternal threads of said screw being of different pitch, a threaded studmovable along the threaded drilled axis of said screw, a metal striphaving one end rigidly attached to an end of said stud, the other end ofsaid metal strip difference between the external and internal threadpitches of said screw.

3. In a magnetic core of the bent strip type having two laminatedmagnetic core sections of generally rectangular shape, with one leg ofeach of said rectangular core sections adjacent one leg of said othercore section, said two adjacent legs together forming a composite legabout which an electrical winding is placed, an air gap intermediate ofthe longitudinal dimension of said composite leg, means for adjustingthe thickness of said air gap comprising a metallic strip having one endrigidly attached to one section of said composite leg on one side ofsaid air gap, said metallic strip being interposed between said adjacentlegs of said core sections, a stud rigidly attached to the other end ofsaid metallic strip, a casing surrounding said magnetic core, anexternally threaded screw rotatable in said casing, said screw beingaxially drilled and threaded, the axial threads and external threads ofsaid screw being of a different pitch, said stud being threaded at oneend and engageable with the axial threads of said screw, rotation ofsaid screw to cause axial advancement of said screw in one directioncausing axial motion of said stud in an opposite direction, therebycausing a motion of said section of said composite leg attached to saidmetallic strip equal to the differential motion between said screw andsaid stud, the section of said composite leg on the opposite side of theair gap to the point of attachment of said metallic strip being rigidlybraced in a stationary position with respect to said casing, with meansfor bracing said last-mentioned section of said composite leg comprisinga generally S-shaped brace member which is rigidly attached to saidlast-mentioned section of said composite leg and is also rigidlyattached to said casing, said S-shaped brace member having a main bodyportion lying between said adjacent core legs and extending forsubstantially the entire length of said legs in a plane substantiallyparallel to the plane thereof, said main body portion of said bracemember being apertured adjacent said section of said composite leg towhich said strip member is attached to receive said strip member, thetwo oppositely disposed longitudinally-extending edges of said bracemember being bent in opposite directions substantially perpendicularlyto the main body portion of said brace member, said respectivelongitudinally-extending edges each embracing the edge of a difierentone of said two adjacent legs.

RALPH G. SCHLAWIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,236,292 Kirk Mar. 25, 19412,338,271 Ulanet Jan. 4, 1944 2,446,624 Allison Aug. 8, 1948 2,482,471Dowell Sept. 20, 1949

